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A-level Chemistry > Chapter 13 Alkenes > Flashcards

Chapter 13 Alkenes Flashcards

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1
Q

what is an alkene

A

unsaturated hydrocarbon that can be aliphatic or alicyclic

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2
Q

what is the general formula of an alkene

A

CnH2n

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3
Q

what is the shape and bond angle for an alkene aroound one of the carbon atoms

A

trigonal planar

120

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4
Q

what are the bonds in each carbon atom in the alkene bond

A

3 sigma bonds

1 Pi bond

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5
Q

what is a Pi bond

A

Bond formed due to a sideways overlap of p orbitals

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6
Q

why do the carbons have a Pi bond

A

3 of the electrons in the p orbital overlap with the other atoms electrons to produce a sigma bond. This leaves one electron per carbon that are above and below the C-C sigma bond so produces a sideways overlap

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7
Q

what happens to the bonds when an alkene reacts

A

the Pi bond is weaker than the sigma bond so less energy is required to break it causing the electrons in the Pi bond to move away breaking the double bond

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8
Q

what is a Stereoisomer

A

Isomers of molecules with different arrangements in space that they take up

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9
Q

what two notations can be used to distinguish Stereoisomers

A

E/Z

cis/trans

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10
Q

which symbols can you use when the two priority groups are on the same side

A

cis-

Z-

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11
Q

which symbols can you use when the two priority groups are on opposite sides

A

trans-

E-

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12
Q

when do you use cis/trans

A

when one of the attached groups on each carbon atom is a hydrogen

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13
Q

when do you use E/Z

A

when one or either of the attached groups on at least one carbon atom is not a hydorgen

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14
Q

what is the Cahn-Ingold-Prelog (CIP) rules

A

Naming system for stereisomers that focuses on the atomic number of atoms attached to each carbon in the double bond

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15
Q

How does the CIP rules work

A

Find the atomic number of each atom attached to one carbon atom. The one with the highest number has priority. Then use the correct symbol based on the relative positions of the two priority atoms

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16
Q

why are Pi bonds weaker than sigma bonds

A

They are more exposed and spread out than sigma bonds

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17
Q

why are the Pi bonds useful for alkenes

A

they are why alkenes are far more reactive by turning the one of the carbon atoms into a carbocation allowing for electrophilic addition reactions

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18
Q

what happens during the electrophilic addition reaction for alkenes

A

> electrophilic atom is attracted to the alkene and bonds to one of the carbon atoms by taking the electrons from the Pi bond
this makes the other carbon a carbocation
The carbocation bonds to a negatively charged atom

19
Q

what is a carbocation

A

Positively charged carbon ions that are highly reactive and very unstable

20
Q

what Markownikoff’s rule

A

if you have a two step process with carbocation intermediate the preferred route is governed by the stability of the carbocation

21
Q

what are the four carbocations

A

tertiary three C-C bonds most stable
secondary two C-C bonds
primary one C-C bond
methyl no C-C bonds

22
Q

what is the word formula for the adddition of hydrohalides

A

Alkene + hydrohalide –> haloalkane

23
Q

what is the word formula for the addition of halogens

A

Alkene + halogens –> dihaloalkanes

24
Q

what is the word formula for the addition of steam

A

Alkene + steam –> Alcohol

25
Q

What are three conditions for the addition of steam reaction

A

> 100C
Phosphoric acid catalyst
High pressure

26
Q

what is the word formula for the addition of hydrogen reaction

A

Alkene + Hydrogen –> Alkane

27
Q

What are the two conditions required for a hydrogenation of alkene reaction

A

High pressure

Nickel or Platinum catalyst

28
Q

what are the physical property differences between saturated and unsaturated solids

A

Saturated solids have tetrahedral shape and pack together very well increasing the number of stronger IMF
Unsaturated solids has trigonal planar shape with branching so doesn’t pack together as well making IMF weaker

29
Q

what is a HDP

A

high density polymer

30
Q

what is a VLDP

A

very low density polymer

31
Q

how are HDPs made

A

packing chains close together with lots and lots of induced dipole-dipole bonds making it strong, rigid and inflexible

32
Q

how are VLDPs made

A

packing chains in random arrangement so there are few IMF so is flexible, low density and cheap

33
Q

what part of the alkene monomer reacts to make an addition polymer

A

double bond only reacts almost acts akin to a spectator ion almost

34
Q

what is a polymer

A

Long chain of small molecules called monomers

35
Q

what are 3 important details about hydrocarbon polymers

A

> different functional groups change chemical and physical properties
altering the shape of the polymer changes physical properties due to number of IMFs
branching weakens IMF by pushing molecules further apart

36
Q

what are the two types of polymers

A

addition

condensation

37
Q

what is an addition polymer

A

unsaturated monomers where Pi bonds break and electrons used to form links between monomers

38
Q

what is the problem with disposing of polymers

A

most don’t biodegrade so cause immense environmental damage

39
Q

what are the 6 methods of disposing of polymers

A 
>Incineration
>recycling
>using waste polymers as fuel
>feedstock recycling
>bioplastics
>photodegradeable polymer
40
Q

what is the process of recycling polymers

A

polymers are sorted by type then washed and dried before being melted down then being reused for new polymer products

41
Q

what is the process of using waste polymers as fuel

A

polymers are burnt releasing the vast amount of energy stored in their bonds using it to generate steam to turn turbines at power plants

42
Q

what is feedstock recycling

A

polymers are turned back into products resembling crude oil based compounds and are resued to make any polymer based product

43
Q

what are bioplastics

A

polymers that have additives that allow it to biodegrade naturally in a landfill not damaging the environment or are naturally biodegradable plant based polymers

44
Q

what are photodegradeable polymers

A

polymers that are oil based weakening the bonds in the polymer allowing to biodegrade when exposed to energy like UV light

A-level Chemistry (19 decks)

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